Composition and method of inhibiting corrosion of ferrous metals by aminestabilized unsaturated chlorinated hydrocarbons



rates atent sheath Patented Apr. 24, 192

fine COMPOSITION AND IVETHOD F INHIBITING 'CDRROSION 0F FERROUS" METALS BY AMINE- STALBHJZED UNSATURATED CHLORINATED HYDROCARBONS (USING OXHVIES) Wilbur H. Petering and William A. Callahan, Detroit, Mich, assignors to Detrex Chemical Industries, Inc, Detroit, Mich, a corporation of Michigan No Drawing. Filed June 10, 1958, Ser. No. 741,002

16 Claims. (CL 252- 171) 1 This application is a continuation-in-part of applicants copending application Serial No; 445,474, filed July 23, 1954, and now abandoned.

This invention relates to a composition and method of inhibiting the corrosion of ferrous metals by aminestabilized, unsaturated chlorinated hydrocarbons, particularly those chlorinated hydrocarbons which decompose under the influence of metals or oxygen to form acidic products. Among the chlorinated hydrocarbons inhibited in accordance with this invention are the unsaturated chlorinated hydrocarbons such as 1,2 dichloroethylene, trichlorethylene, perchlorethylene, the chloropropylenes, the chlorobutylenes and the chlorobutadienes. All such unsaturated chlorinatedhydrocarbons have low molecular weights and are subject to decomposition by metals or oxygen, or in their presence, and this decomposition is accelerated by light and heat.

It is conventional in the art to add stabilizers of various types to chlorinated hydrocarbons. Among the accepted stabilizers are the phenolic compounds, aryl amines, and various azo compounds. However, the use of such compounds is quite limited except in the case of a few of the higher boiling chlorinated hydrocarbons, since the stabilizers also have relatively high boiling points. A wide difference in boiling points between the solvent and the stabilizer is undesirable because of the difficulty of stabilizing the vapor phase, and it is desirable to provide a combination of solvent and stabilizer not having a wide difference in boiling points.

v The organic amine bases have enjoyed widespread use as stabilizers for unsaturated chlorinated hydrocarbons. Such bases, including primary aliphatic amines having the nitrogen in the ring such as pyridine and the like are disclosed in the patents to Dinley, Numbers 2,096,735, 2,096,736 and 2,096,737. Under many conditions the primary aliphatic and cyclic amine bases disclosed in the Din'ley patents are highly elfective and desirable stabilizers for chlorinated hydrocarbons.

In the manufacture of the unsaturated chlorinated hy drocarbons as trichlorethylene, for example, the recovery of a neutral, sweet, relatively pure product isalmost impossible without the use of a stabilizer such as these amines. The amine stabilizer should be present in the refining operation, as distinguished from adding amine to the refined product, and the amine should be volatile with the chlorinated hydrocarbon and therefore carry over from the refining operation into the refined product. Unless a. neutral, sweet product is obtained when the solvent is refined, subsequent attempts to stabilize the solvent tain metals of the iron'group. lt has now been discov NH radical and basic cyclic compounds characterized by ered that the lower boiling unsaturated chlorinated hydrocarbons, when stabilized with certain of the conventional organic amines, such amines having boiling points which are not Widely different from the boiling point of v the chlorinated hydrocarbon, appear to enter into a complex reaction when exposed to one of those metals. The reaction appears to be metal-induced, causing a progressive decomposition of the chlorinated. hydrocarbons. The reaction which occurs in the presence of conventional amines causes attack on the metal, rapid loss of amine stabilizer and the development of acidic materials, and apparently the series of reactions producing the decomposition requires the presence of the amine.

The corrosive action of the amines appears to be related to certain specific metals, especially iron (also in its com: mon alloyed form as steel) and copper (alone or in its alloyed form as brass). On the other hand, aluminum, which is known to be an agent for metal induced decomposition in some cases, does not initiate the corrosion reaction in amine-stabilized systems.

In referring to amines in the foregoing paragraph, we have used the term in its broad sense. The other organic bases specified in the Dinley patents, including cyclic compounds characterized by nitrogen in the ring, such as pyridine and morpholine, for example, are included within the meaning of this term. Among the suitable amines which are listed in the examples set forth hereinafter, and which are accordingly suitable in the practice of this invention are pyridine, di sec. butylamine, diisopropylamine, diethylamine, n-butylamine, amylamine, methyl pyridine, n-methyl morpholine, triethylamine, and hexylamine.

The exact mechanism by which the amine reacts with the chlorinated hydrocarbon in the presence of the metal is not completely known or understood. It may be that the amine, being a strong base, that is, a Lewis base or electron donor, either forms a covalent bond with one carbon atom of the unsaturated chlorinated hydrocarbon, and the resulting fragment reacts with the metal, or, in the case of chlorinated hydrocarbons containing hydrogen, the amine may react by first removing a hydrogen to yield ionic fragments, which in turn are reactive toward metalsthe end products of such reactions being more or less complex metal-organic chloro compounds. Then again, the metal may be the initiator of the set of reactions which involve the amine and the chlorinated solvent.

One explanation for the reaction is that the unsaturated chlorinated compound, being arnphoteric, that is, having one carbon basic and the other acid at the unsaturated bond, and the amine being basic, that is, a Lewis base or electron donor, forms a covalent bond at the acidic carbon leaving the resultant fragment basic and that a metal brings about chelation. It may be that the basic fragment or electron donor amine itself holds the metal in the active state as opposed to the passive state (according to the Electron Theory of Corrosion in Corrosion Handbook by Uhlig) so that the active metal reacts with the solvent or the amine stabilizer or the fragment which is basic, forming organo-metallics which are agents which hasten normal oxidation or at least remove the stabilizer as such and thus reduce the concentration of stabilizer to sub minimal levels, and at the same time cause serious attack on or corrosion of the metal. In any event, serious corrosion problems are encountered when a lowboiling unsaturated chlorinated hydrocarbon is stabilized with an amine and the product exposed to a ferrous metal, or copper, particularly when the hydrocarbon is a hot, bone-dry liquid. 7

It is accordingly an obiectof this invention to provide a composition and method for overcoming the foregoing disadvantages. Still another object is to provide an improved corrosion-resistant stabilizer composition for the lower boiling unsaturated chlorinated hydrocarbons. Other objects and advantages of this invention will further appear hereinafter.

In accordance with this invention, the corrosive action of the organic amine in the presence of metals in the chlorinated hydrocarbon is overcome by incorporating into the mixture a small amount of an oxime which interferes with the corrosive action of the amine in the presence of ferrous metals. The oxime does not interfere with the stabilizing action of the amine, or its ability to act as an alkaline material or to act as a reducing agent. It appears that the oximes of the present invention act to retard or interfere with the corrosive activity of the amine by either hindering the amine itself, or by forming a protective layer over the surface of the metal. In the former case the amount of oxime required to control the action of the amine is related to the amount of amine used, while in the latter case the amount of oxime required is related to the surface area of the metal exposed to the solvent and amine.

It has been found that in a few cases, if the amine, when used in the usual stabilizing'concentration, reacts With the chlorinated solvent and the metal exposed to the stabilizer and solvent, the activity can be reduced by using a greatly increased concentration of stabilizer as, for example, about ten times the usual stabilizing amount. It is believed that the very large amount of amine stabilizer is able to form a protective coating over the metal surface, thus interfering in the reaction between the amine, solvent and metal. That method of controlling the activity of amine is not desirable because such large amounts of amine add to the cost of stabilizing the solvent; moreover, if under some condition the concentration of amine should become depleted, the concentration would fall into that level where the reactivity of the amine would rapidly increase and the corrosion difficulties mentioned above would be encountered.

The oximes in accordance with this invention include at least one =N-OH group. The following examples are illustrative:

(l) Dimethyl glyoxime (2) Formaldoxime (3) Acetaldoxime (4) Acetoxime (5) Crotonaldoxime (6) Propionaldoxime In accordance with this invention, the crude unsaturated chlorinated hydrocarbon, prior to the refining operation, is combined with a stabilizing proportion of amine. The stabilized product is combined with an inhibitive proportion of an oxime selected from the group consisting of the oximes listed above and their equivalent oximes. The resulting mixture is heated in a still, which volatilizes the amine and chlorinated hydrocarbon but not the oxime. Since the severe corrosion problem occurs in the substantially anhydrous liquid phase, the oxime is retained at the location where it is most needed. At the same time, the amine stabilizes the chlorinated hydrocarbon in the liquid and vapor phases.

Unsaturated chlorinated hydrocarbons such as trichlorethylene and perchlorethylene are widely used as degreasing solvents, cleaners and the like. For example, ferrous metals are degreased commercially by subjecting them to liquid and to vapor phase chlorinated hydrocarbons. Since the liquid hydrocarbon is heated and contains amine, and since it is anhydrous and in the liquid phase, there is some danger of corrosion of the degreasing apparatus or of the metal immersed in the liquid. Accordingly, it is commercially advantageous to provide a chlorinated hydrocarbon solvent which contains both an amine and an oxime in accordance with this invention.

It is well known that the proportions of amine stabilizers may vary from trace values (such as .01% by weight or less) to as high as 1.0% by weight, based on the weight of the chlorinated hydrocarbon. However, a range of the order of about .02.20% by weight represents the proportions considered commercially preferable in most amine-stabilized chlorinated hydrocarbons. Amine stabilizers have been well known and extensively used, and different amines have been used in different proportions for diiferent chlorinated hydrocarbons. The art is well aware of the proper proportions of each specific amine stabilizer in each specific chlorinated hydrocarbon, and such proportions are conventionally referred to as stabilizing proportions, and are so defined herein.

The proportions of the oxime may be varied from about .01% by weight to about 5% by weight, but a range of about .01-.15% by weight is preferred. Such proportions are referred to as inhibitive proportions, and are so defined herein. Preferably, the weight of oxime is about 1-5 times the weight of amine stabilizer. The effect of these oximes is shown in the results of tests described below:

A chlorinated hydrocarbon is refluxed in the presence of a weighed piece of metal. A stabilizing amount of an amine is added and the solvent refluxed continuously. After refluxing for at least 48 hours the solvent is titrated for alkalinity and the metal weighed to determine the loss of metal. Similar tests, in which an inhibiting amount of oxime has been added along with the amine, are run. Also tests, in which the oxime is used alone without amine,

are run.

The foregoing reflux test has been used in industry to evaluate chlorinated solvents for use in such processes as degreasing. Since the test is not particularly severe it does not evaluate stability of the solvent or the eflicacy of the stabilizer used. Therefore in the absence of a stabilizer or in the presence of a weak stabilizer, the breakdown of the solvent is not particularly rapid. Therefore, because the test duplicates a continuous refluxing condition which would exist under normal conditions of use, it serves as a valuable tool in showing the reaction of the amine and solvent in the presence of metal.

The inhibitory effect on steel of dimethyl glyoxime in perchlorethylene is shown in the following results:

Loss of Oxime Hours Alka- Loss of Amine Per- Added, of linity, Metal,

cent Percent Test p.p.m. MgrnJFt. 2

Triethylamine. .02 None 16 71.0 Heavy Corrosion. Do .02 .05%Di- 72 21.4 No Cormethyl rosion. Glyoxime.

In addition to the oximes referred to above, we may also employ in the practice of the present invention the following oximes in the amounts and proportions indicated:

Also butyraldoxime in the range of .05 to 1% by weight of the solvent used.

Since the exact amount of oxime and amine within the range specified is not critical, it is intended that such man In terials and amounts be taken as specific examples of the practice of the present invention.

Having thus described our invention, we claim:

1. A stabilized solvent which is substantially non-corrosive to ferrous metals consisting essentially of a volatile low-boiling low molecular weight unsaturated chlorinated hydrocarbon which is normally subject to decomposition by metals and oxygen containing an organic amine selected from the group consisting of pyridine, di sec. butylamine, diisopropylamine, diethylamine, n-butylamine, amylamine, methyl pyridine, N-methyl morpholine, triethylamine, and hexylamine, and having a boiling point near that of the chlorinated hydrocarbon in a stabilizing proportion in an amount of from about .01% to about 1.0% by weight of said solvent, said amine-stabilized solvent in the presence of ferrous metals causing metal corrosion, in combination with an inhibitor for said ferrous metal-amine corrosion comprising an oxime having from one to two =NOH groups and having from one to four carbon atoms, said corrosion inhibitor being present in an amount from about .01%-5% by weight.

2. The stabilized solvent defined in claim 1 wherein the oxime is dimethyl glyoxime.

3. The Stabilized solvent defined in claim 1 wherein the oxime is formaldoxime.

4. The stabilized solvent defined in claim 1 wherein the oxime is acetaldoxirne.

5. The stabilized solvent defined in claim 1 wherein the oxime is acetoxime.

6. The stabilized solvent defined in claim 1 wherein the oxime is crotonaldoxime. t

7. The stabilized solvent defined in claim 1 wherein the oxime is propionaldoxime.

8. In a process wherein a volatile unsaturated low molecular weight chlorinated hydrocarbon is exposed in the hot anhydrous liquid state to a ferrous metal, said hydrocarbon including a stabilizing proportion of an organic amine selected from the. group consisting of pyridine, di sec. butylamine, diisopropylamine, diethylamine, n-butylamine, amylamine, methyl pyridine, N-methyl morpholine, triethylamine, and hexylamine amine in an amount of from about .0l% to about 1.0% by weight of said chlorinated hydrocarbon which normally reacts with the chlorinated hydrocarbon and ferrous metal in the presence of said metal to corrode said metal, the improvement which comprises incorporating into the said chlorinated hydrocarbon and amine about .01-5% by weight of an inhibitor for said ferrous metal-amine corrosion comprising an oxime having from one to two =NOH groups and having from one to four carbon atoms.

9. The process defined in claim 8 wherein the oxime is dimethyl glyoxime.

10. The process defined in claim 8 wherein the oxime is formaldoxime.

11. The process defined in claim 8 wherein the oxime is acetaldoxime.

12. The process defined in claim 8 wherein the oxime is acetoxime.

13. The process defined in claim 8 wherein the oxime is crotonaldoxime.

14. The process defined in claim 8 wherein the oxime is propionaldoxime.

15. A stabilized solvent which is substantially non-corrosive to ferrous metals consisting essentially of a volatile low-boiling low molecular weight unsaturated chlorinated hydrocarbon which is normally subject to decomposition by metals and oxygen, containing as a stabilizer about .01.20% of an organic amine selected from the group consisting of pyridine, di sec. butylamine, diisopropylamine, diethylamine, n-butylamine, amylamine, methyl pyridine, N-methyl morpholine, triethylamine, and hexylamine, said amine having a boiling point near that of the chlorinated hydrocarbon, said amine-stabilized solvent in the presence of ferrous metals causing metal corrosion, in combination with an inhibitor for said ferrous metal-amine corrosion comprising an oxime having from one to two =NOH groups and having from one to four carbon atoms, said corrosion inhibitor being present in an amount from about .0l%5% by weight.

16. In a process wherein a volatile unsaturated low molecular weight chlorinated hydrocarbon is exposed in the hot anhydrous liquid state to a ferrous metal, said bydrocarbon including as a stabilizer about .0l%.20% by weight of an organic amine selected from the group consisting of pyridine, di sec. butylamine, diisopropylamine, diethylamine, n-butylamine, amylamine, methyl pyridine, N-methyl morpholine, triethylamine, and hexylamine which normally reacts with the chlorinated hydrocarbon and ferrous metal in the presence of said metal to corrode said metal, the improvement which comprises incorporating into the said chlorinated hydrocarbon and amine about .01%5% by weight of an inhibitor for said ferrous metalamine corrosion comprising an oxime having from one to two =NOH groups and having from one to four carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,031,411 April 24, 1962 Wilbur H. Petering et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 41, strike out "amine".

Signed and sealed this 27th day of November 1962.

(SEAL) Attest:

ESTON c. JOHNSON fififiiixhkx DAVID L- LADD Attesting Officer Commissioner of Patents 

1. A STABILIZED SOLVENT WHICH IS SUBSTANTIALLY NON-CORROSIVE TO FERROUS METALS CONSISTING ESSENTIALLY OF A VOLATILE LOW-BOILING LOW MOLECULAR WEIGHT UNSATURATED CHLORINATED HYDROCARBON WHICH IS NORMALLY SUBJECT TO DECOMPOSITION BY METALS AND OXYGEN CONTAINING AN ORGANIC AMINE SELECTED FROM THE GROUP CONSISTING OF PYRIDINE, DI SEC, BUTYLAMINE, DIISOPROPYLAMINE, DIETHYLAMINE, N-BUTYLAMINE, AMYLAMINE, METHYL PYRIDINE, N-METHYL MORPHOLINE, TRIETHYLAMINE, AND HEXYLAMINE, AND HAVING A BOILING POINT NEAR THAT OF THE CHLORINATED HYDROCARBON IN A STABILIZING PROPORTION IN AN AMOUNT OF FROM ABOUT .01% TO ABOUT 1.0% BY WEIGHT OF SAID SOLVENT, SAID AMINE-STABILIZED SOLVENT IN THE PRESENCE OF FERROUS METALS CAUSING METAL CORROSION, IN COMBINATION WITH AN INHIBITOR FOR SAID FERROUS METAL-AMINE CORROSION COMPRISING AN OXIME HAVING FROM ONE TO TWO=N-OH GROUPS AND HAVING FROM ONE TO FOUR CARBON ATOMS, SAID CORROSION INHIBITOR BEING PRESENT IN AN AMOUNT FROM ABOUT .01%-5% BY WEIGHT. 